Wood-free fiber compositions and uses in paperboard packaging

ABSTRACT

A paperboard packaging material includes a top layer including non-wood fibers blended with wood fibers, wherein the non-wood fibers are 5% to 100% of the top layer; a back layer including non-wood fibers blended with wood fibers, wherein the non-wood fibers are 5% to 100% of the back layer; and a middle layer disposed between the top and back layers. The middle layer can include 5% to 100% non-wood filler fibers. The non-wood filler fibers can be wheat straw. The non-wood fibers can be bamboo.

BACKGROUND

The present disclosure relates to the use of non-wood alternative natural fibers in corrugated medium for paperboard packaging. A replacement of the conventional hardwood fiber is achieved by a hybrid fibrous composition that provides sufficient mechanical strength for paperboard packaging applications.

Traditionally pulp derived from fast growing trees, such as pine, has been used as the raw material for paperboard packaging. In recent years, the use of recycled, old corrugated container (OCC) material has grown in popularity because of concerns about environmental sustainability. The OCC, however, frequently requires repulping and de-inking processes. As such, the recycled fibers get shortened, weakened, and contaminated as the number of recycles increases. Coupled with an increased demand and use of recycled fiber by many producers, the cost of recycled fiber has also increased. The move toward single stream recycling is causing an increase in contamination (staples, plastic tapes, and hot melt adhesives) of and the mixing of fibers in the existing recovered fiber streams. Critical performance requirements such as strength (compression, edge crush, burst, and tensile strength), stiffness, rigidity, moisture resistance, grease resistance, and freeze/thaw tolerance can be more difficult to achieve with recycled paper or paperboard.

Solid unbleached sulfate (SUS) or solid bleached sulfate (SBS) are premium paperboard grades that are produced from a furnish containing at least 80 percent virgin long and short bleached wood pulp. Most bleached paperboard is coated with a thin layer of kaolin clay to improve its surface smoothness for printing. SBS is most popular in the United States. Unfortunately, supply of NBSK (Northern bleached softwood Kraft) as a long fiber is under significant pressure both economically and environmentally. As such, the cost of NBSK fiber has escalated significantly creating a need to find alternatives to optimize paperboard strength.

These approaches rely on tree-based fibers. The ability to use fibrous feedstock that grows in a shorter lifecycle and to use of residuals from agricultural or industrial processing can help to fulfill corporate sustainability goals and reduce environmental impact on forests as well as carbon footprint (measured in eCO2 units).

Pulping processes for non-wood natural fibers are raw material dependent and detailed steps can be found in Sridach, W. (2010), The Environmentally Benign Pulping Process of Non-wood Fibers, Suranaree J. Sci. Technol., 17(2), 105-123, and U.S. Pat. No. 6,302,997 B1 to Hurter and Byrd. Alternative non-wood natural fibers such as using field crop fibers or agricultural residues instead of wood fibers are considered as being more sustainable. Examples of those raw natural materials are kenaf, flax, bamboo, cotton, jute, hemp, sisal, bagasse, corn stover, rice straw, wheat straw, hesperaloe, switchgrass, reed, arundo donax and marine or fresh water algae/seaweeds or aquatic plants such as water hyacinth. Non-wood fiber sources account for about 5-10% of global pulp production, for a variety of reasons, including seasonal availability, problems with chemical recovery, brightness of the pulp, silica content, etc. However, they provide an option for which any product manufacturers can explore to add a green component into their final products.

Hybrid fiber compositions including non-wood alternative natural fibers such as those derived from seaweed, algae, corn stover, wheat straw, rice straw, bamboo, kenaf, and the like can be an option to resolve such aforementioned issues by creating tree-free products.

A previous approach (see U.S. Pat. No. 1,829,852 to Darling) used chopped wheat straw (not a fiber per se) to make cardboard. In another approach (see U.S. Patent Publication No. 2006/0070295 to Huang and Peng) described a non-woody fiber (corn or wheat) mulching mat for weed control in agricultural plantation and cultivation. Finally, chitosan in addition to agricultural residual fibers was used to improve the flat crush resistance of a corrugating medium (see U.S. Pat. No. 4,102,738 to Dzurik).

Therefore, there exists a need for providing wood-alternative pulp materials to replace conventional fiber materials used in paperboard packaging. Additionally, there is a growing need for stronger, lighter weight materials that allow for packaging weight reduction. Although some previous efforts have attempted to use alternative fibers to produce construction- and furniture-applied composite boards, there is a lack of sustainable attempts to produce non-wood natural fiber to be used in paperboard packaging applications. As a result, the present disclosure fills such gaps by providing wood-alternative materials that can be used for environmentally-sustainable paperboard packaging.

SUMMARY

The present disclosure is directed to a paperboard packaging material including a top layer including non-wood fibers blended with wood fibers, wherein the non-wood fibers are 5% to 100% of the top layer; a back layer including non-wood fibers blended with wood fibers, wherein the non-wood fibers are 5% to 100% of the back layer; and a middle layer disposed between the top and back layers. The middle layer can include 5% to 100% non-wood filler fibers. The non-wood filler fibers can be selected from corn stover, straw, other land-based natural fibers, and combinations thereof. The straw can be selected from the group consisting of wheat, rice, oat, barley, rye, flax, grass, and combinations thereof. The other land-based natural fibers are selected from flax, bamboo, cotton, jute, hemp, sisal, bagasse, kenaf, hesperaloe, switchgrass, miscanthus, and combinations thereof. The non-wood filler fibers can be wheat straw. The non-wood fibers can be bamboo.

The present disclosure is also directed to a paperboard packaging material including a top layer including non-wood fibers blended with wood fibers, wherein the non-wood fibers are 50% to 85% of the top layer, wherein the non-wood fibers are bamboo; a back layer including non-wood fibers blended with wood fibers, wherein the non-wood fibers are 50% to 85% of the back layer, wherein the non-wood fibers are bamboo; and a middle layer disposed between the top and back layers.

The present disclosure is also directed to a paperboard packaging material including a top layer including non-wood fibers blended with wood fibers, wherein the non-wood fibers are 50% to 85% of the top layer, wherein the non-wood fibers are bamboo; a back layer including non-wood fibers blended with wood fibers, wherein the non-wood fibers are 50% to 85% of the back layer, wherein the non-wood fibers are bamboo; and a middle layer disposed between the top and back layers, wherein the middle layer includes 5% to 100% non-wood filler fibers.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and aspects of the present disclosure and the manner of attaining them will become more apparent, and the disclosure itself will be better understood by reference to the following description, appended claims and accompanying drawings, where:

FIG. 1 shows a schematic illustration of a typical paperboard structure;

FIG. 2 shows a micrograph paperboard sectional view by Broad Ion Beam technique (150×); and

FIG. 3 shows a micrograph paperboard sectional view by SEM C-Stain of paperboard of the present application.

Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present disclosure. The drawings are representational and are not necessarily drawn to scale. Certain proportions thereof might be exaggerated, while others might be minimized.

DETAILED DESCRIPTION

While the specification concludes with the claims particularly pointing out and distinctly claiming the disclosure, it is believed that the present disclosure will be better understood from the following description.

As used herein, “comprising” means that other steps and other ingredients that do not affect the end result can be added. This term encompasses the terms “consisting of” and “consisting essentially of.” The compositions and methods/processes of the present disclosure can comprise, consist of, and consist essentially of the essential elements and limitations of the disclosure described herein, as well as any of the additional or optional ingredients, components, steps, or limitations described herein.

As used herein, the terms “non-wood,” “tree-free,” and “wood alternative” generally refer to processing residuals from agricultural crops such as wheat straw, wetland non-tree plants such as bulrush, aquatic plants such as water hyacinth, microalgae such as Spirulina, and macroalgae seaweeds such as red or brown algae. Examples of non-wood natural materials of the present disclosure include, but are not limited to, wheat straw, rice straw, flax, kenaf, bamboo, cotton, jute, hemp, sisal, bagasse, hesperaloe, switchgrass, miscanthus, marine or freshwater algae/seaweeds, and combinations thereof.

As used herein, the term “OCC” refers to old corrugated containers that have layers of paper glued together with a fluted inner layer. This is the material used to make corrugated cardboard boxes (the most recycled product in the country). Four main components of the OCC pulps are unbleached softwood Kraft pulp (mainly from the linerboard), semi-chemical hardwood pulp (from the fluted medium), starch (as an adhesive), and water (often 8% or more).

As used herein, the term “pulp” or “pulp fiber” refers to fibrous material obtained through conventional pulping processes known in the arts. This can be for woody and non-woody materials.

As used herein, the term “fines” refer to the fraction that passes through a 200 mesh screen (75 μm). The median size of fines is a few microns. Fines consist of cellulose, hemicellulose, lignin, and extractives. There are two types of the fines: primary and secondary fines. The primary fines content seems to be a genetic characteristic of the plant. For hardwood pulp, it is about 20% to about 40%, whereas for wheat straw, it is about 38% to about 50%. The secondary fines are pieces of fibrils from the outer layers of fibers that are broken off during refining.

As used herein, the term “basis weight” generally refers to the weight per unit area of paperboard. Basis weight is measured herein using TAPPI test method T-220. A sheet of pulp, commonly 30 cm×30 cm or of another convenient dimension is weighed and then dried to determine the solids content. The area of the sheet is then determined and the ratio of the dried weight to the sheet area is reported as the basis weight in grams per square meter (gsm).

As used herein, the term “Tensile Index” is expressed in Nm/g and refers to the quotient of tensile strength, generally expressed in Newton-meters (N/m) divided by basis weight.

As used herein, the term “Burst Index” refers to the quotient of burst strength, generally expressed in kilopascals (kPa) divided by basis weight, generally expressed in grams per square meter (gsm).

As used herein, the term “ring crush” refers to the resistance of the paper and paperboard to edgewise compression, generally expressed in kilonewton per meter (kN/m).

As used herein, the term “compression” refers to the ability of shipping containers to resist external compressive forces, which is related to the stacking strength of the containers being subjected to forces encountered during transportation and warehousing. It is generally expressed in Newton (N).

As used herein, the term “edge crush” refers to the edgewise compression strength, generally expressed in kilonewton per meter (kN/m).

As used herein the term “web-forming apparatus” generally includes fourdrinier former, twin wire former, cylinder machine, press former, crescent former, and the like, known to those skilled in the arts.

As used herein the term “Canadian standard freeness” (CSF) refers generally to the rate at which slurry of fibers drains and is measured as described in TAPPI standard test method T 227 OM-09. The unit for the CSF is mL.

FIG. 1 schematically shows a structure of paperboard of this invention, where the middle layer 10 uses BCTMP and the top and back layers 20, 30 use NBKP and LBKP. In this example, calcium carbonate is used for the paperboard coating 40. The coating materials applied on the top layer 20 is three times that of those applied on the back layer 30.

The invention describes the use of bamboo to replace a portion of the virgin long wood fiber in the top and back layers 20, 30. Optionally, the middle layer 10 may also be replaced by another alternative non-wood fiber, such as wheat straw.

Bamboo can be used to replace a portion of the virgin long wood fiber in the top and back layers 20, 30 of a multilayered premium paperboard structure. Examples described below range from 50 to 85% bamboo in a layer. Optionally, the middle layer 10 can also be replaced by another alternative non-wood fiber, such as wheat straw. Examples described below include 100% wheat straw. Mechanical properties are comparable or better than the control that is composed of all virgin wood pulp fibers. The paperboard can be used for product packaging in support of sustainability goals at equivalent or possibly lower cost than current wood-based paperboard.

As stated above, SUS/SBS paperboard is made using virgin wood-based fibers today. However, continuous uses of the long softwood fiber are economically and environmentally challenged. Therefore, a replacement of the wood-based long fiber fulfills unmet business needs. Long non-wood natural fibers selected from bamboo species are not customarily used in top and back layers 20, 30 in the paperboard. This disclosure describes the use of bamboo in paperboard, which is previously unknown and unpracticed. The paperboard sheet containing bamboo can then be coated for printing and converting.

A conventional SUS/SBS paperboard structure is layered. The top and back layers 20, 30 use a mixture of softwood long and hardwood short fibers. The middle layer 10 uses bleached or unbleached chemithermomechanical pulp (CTMP). Typically a coating is applied to the outer surfaces, such as latex, kaolin clay or calcium carbonate. The use of non-wood alternative natural fibers such as bamboo is an option to replace NBKP (top and back layers 20, 30) in paperboard to create new packaging materials. This disclosure relates to multi-layer paper and paperboard products in which top and back plies are formed using bamboo or a combination of bamboo leaf bleached Kraft pulp (LBKP) and NBKP fibers. The efficacy of such an application is an unexpected result—that using bamboo to replace virgin wood fibers provides superior mechanical properties in comparison to a control that is composed of all virgin wood pulp fibers. The data shown in this disclosure demonstrates the ability to use alternative fibers for product packaging.

The following two documents describe the use of bamboo in tissue products:

U.S. Pat. No. 8,778,505 Tissue product comprising bamboo U.S. Pat. No. 8,524,374 Tissue Product comprising bamboo The following two documents describe the use of non-wood alternative fibers in containerboard (corrugated cardboard):

US2014093705 Tree-Free Fiber Compositions and Uses in Paperboard Packaging US2014093704 Hybrid Fiber Compositions and Uses in Paperboard Packaging

A major problem affecting pulp and paper industries worldwide is the increasing cost of suitable wood fiber resulting from concerns about competing uses for forest lands, environmental impact of forest operations, and sustainable forest management. In recent years major tissue manufacturers have been motivated to examine alternative utilization of non-wood natural fibers for product manufacturing due to sustainability issues related to commodity pulp. Reducing reliance on commodity wood pulp can also alleviate pressure from NGO and consumers who prefer to use green products. Use of the recycled fibers, however, in a variety of products is technically limited by the end product quality acceptable to users.

Recycled fibers can be derived from any paper and board that has been collected for reuse as raw fiber material in paper and board manufacturing. Conversely, commodity wood pulps are classified into softwood pulp derived from softwood trees such as spruce, pine, fir, larch and hemlock, and hardwood pulp derived from hardwood trees such as eucalyptus, aspen and birch.

Pulping processes for non-wood natural fibers are raw-material-dependent; detailed steps can be found in Sridach, W. (2010), The Environmentally Benign Pulping Process of Non-wood Fibers, Suranaree J. Sci. Technol., 17(2), 105-123. For example, red algae pulp can be processed by simple bleaching steps with much less energy and capital cost, partially because there is no presence of lignin (Seo, Y. B. et al. (2010), Red Algae and Their Use in Papermaking, Bioresource Technology, 101, 2549-2553).

Use of alternative non-wood natural fibers such as using field crop fibers and agricultural residues instead of wood fibers is considered more sustainable, due in part to the classification of these materials as by-products of or waste from other processes. Suppliers can pay customers to help them dispose of these materials. Examples of such raw natural materials are kenaf, flax, bamboo, cotton, jute, hemp, sisal, bagasse, corn stover, rice straw, wheat straw, hesperaloe, switchgrass, reed, arundo donax, marine or fresh water algae/seaweeds, or aquatic plants such as water hyacinth. Non-wood fiber sources account for only about 5-10% of global pulp production for a variety of reasons including seasonal availability, problems with chemical recovery, brightness of the pulp, silica content, etc.

The present disclosure describes using at least one non-wood or tree-free alternative pulp material in paperboard packaging to replace a major portion of conventional fiber materials. The composition of the present disclosure includes at least one non-wood alternative pulp material selected from land-based natural fibers, and combinations thereof. Land-based natural fibers can include flax, bamboo, cotton, jute, hemp, sisal, bagasse, kenaf, hesperaloe, switchgrass, miscanthus, and combinations thereof. Individual fibrous material from those non-wood materials can be derived from conventional pulping processes such as thermal mechanical pulping, Kraft pulping, chemical pulping, enzyme-assisted biological pulping or organosolv pulping known in the art.

The pulp material compositions of the present disclosure can include various amounts of non-wood alternative natural pulp fibers. The composition can have a combination of elements where there is at least one non-wood alternative natural pulp fiber alone or it can be combined with a wood pulp fiber. For example, the amount of non-wood alternative natural pulp fibers of the present disclosure can be present in an amount of from about 5%, from about 10%, from about 20%, from about 25%, from about 30% to about 40%, to about 50%, to about 60%, to about 75%, to about 100% by weight of the composition. The pulp material compositions of the present disclosure can also include a hardwood, short fiber pulp in an amount of from about 5%, from about 10%, from about 20%, or from about 30%, to about 40%, to about 50%, to about 60% or to about 70%, by weight of the composition. When the non-wood alternative pulp materials are present alone, in combination with each other or in combination with a wood pulp fiber, the composition can then be used for a paperboard packaging that replaces a portion of conventional fiber materials.

Compositions of the present disclosure can show combinations, although not limited to, wherein the chemical hardwood pulp to non-wood alternative natural pulp ratio can be from about 70:30, from about 60:40, from about 50:50, from about 30:70, from about 5:95 or from about 0:100. Within any of the non-wood alternative natural pulp, there can the use of one type of non-wood alternative natural pulp or two or more in combination.

EXAMPLES

The following examples further describe and demonstrate aspects within the scope of the present disclosure. The examples are given solely for the purpose of illustration and are not to be construed as limitations of the present disclosure, as many variations thereof are possible. The results indicate paperboard can be made totally based on non-wood alternative fibers such as kenaf, wheat straw, miscanthus, corn stover, and bamboo. This disclosure is about tree-free paperboard, which is a significant contrast to the current practice that relies on OCC, hardwood pulp, or a combination of both.

Overview

Two sets of comparative handsheet examples were made. Example 1 as a control sample and example 2 as an inventive sample were made on a dynamic sheet former (available from Fibertech, Sweden). Example 2 includes bamboo at 50% in both the top and back layers 20, 30 and replaces the middle layer 10 with wheat straw.

-   -   Example 1 (control) layer structure/content is 1:1:1         (Pine)/(Pre-consumer Fiber)/(Pine), where Alabama pine is from         GP Cellulose and the recycled pre-consumer fiber is from Fox         River Fiber (brightness >82.9% and freeness >482 mL).     -   Example 2 layer structure/content is 1:1:1 (50/50         Pine/Bamboo)/(Wheat Straw)/(50/50 Pine/Bamboo)

Benefits observed: All mechanical properties are comparable or better than the control of Example 1. Example 2 demonstrated enhanced mechanical strength, including ZD tensile and stiffness. This is surprising as the presence of alternative non-wood fiber typically adversely affects mechanical properties of a composite paperboard.

Example 3 as a control sample and example 4 as an inventive sample were made on a commercial paper machine (IP-Sun, Yanzhou, Shandong, China). Example 4 includes bamboo at 75% in the top layer 20 and 85% in the back layer.

-   -   Example 3 (control) is commercially available StarBlanc C1S         Ivory Board. Its layer structure is approximately 1:4:1 (blend         of two types of Kraft Pulp NBKP/LBKP)/(blend of two types of         Mechanical Pulp APMP/BCTMP and broke)/(blend of two types of         Kraft Pulp NBKP/LBKP). It is coated on both sides. See below for         specifics.     -   Example 4 layer structure is approximately 1:4:1 (25/75         NBKP/Bamboo)/(same middle layer as in example 3)/(15/85         NBKP/Bamboo). It is also coated similarly on both sides.

Benefits observed: All mechanical properties are comparable or better than the control of example 3. The folding strength of example 4 is much better than that of the control of example 3. The smoothness of example 4 is less than half of the value of the control sample, but still much higher than the required level.

Materials

Bamboo pulp was purchased from Xiamen C&D Paper & Pulp Co., Ltd. in Xiamen, China. Northern bleached Kraft pulp (NBKP) is made of softwood fibers such as those pulped from Masson pine, larch, pinus, and spruce. Leaf bleached Kraft pulp (LBKP) is made of hardwood fibers such as those pulped from birch, poplar, basswood, maple and eucalyptus. These materials were purchased from UPM Uruguay in Helsinki, Finland. BCTMP SW pulp was purchased from Panpac Forest Products, Ltd. in Napier, New Zealand. Alkaline peroxide mechanical pulp (APMP) was purchased from Yanzhou Heli Paper Industry Co., Ltd. in Yanzhou, China. Broke is recycled from manufacturing processes. Latex, clay, and ground calcium carbonate were used as coating materials for paperboard manufacturing.

Recycled pre-consumer fiber (Fox River Fiber, De Pere, Wis.), wheat straw (Shandong Pulp and Paper Co. Ltd., Jinan, China) and Alabama pine (GP Cellulose, Atlanta, Ga.) were used to make three layered handsheets using a dynamic handsheet former.

Equipment

The inventive samples were made using a paper machine (PM 18) at IP-Sun in Yanzhou, Shandong, China. A trimmed paperboard width is 3350 mm. PM 18 was equipped with four wires (top ply, under ply, filler ply and back ply).

A layered paper sheet was formed using a dynamic sheet former (Fibertech, Sweden) by pumping the stock (pulp consistency 0.5% or less) from the mixing chest through a transversing nozzle into the rotating drum (1450 rpm) onto the blot paper on top of 100 mesh metal screen, draining the stock to form the sheet, pressing (20 PSI) and dying the sheet at 150° C. The amount of fiber for each layer and additives (if used) could be controlled in the mixing chest prior to pumping.

Example 1

This control paperboard sample contains ⅓ of top layer 20 (pine) and ⅓ filler in the middle (pre-consumer fiber) and ⅓ back layer 30 (pine), respectively. It was formed using the dynamic sheet former. The fiber weight for each layer was determined according the targeted paperboard basis weight of 60 pounds per 1000 square foot (˜300 g/m²) and a diluted suspension (0.5% or less) was prepared in the mixing chest and pumped via the transversing nozzle to the blot paper in the rotating drum. The wet paperboard formed was pressed and dried at 150° C. for about 10 minutes. The testing results are shown in Table 1, which can be used to compare them against the sample of example 2.

Example 2

As shown in Table 1, the sample of example 2 was made using different combinations of pine and bamboo fibers for top and back layers 20, 30. However, the middle layer 10 was completely replaced by wheat straw. The handsheet basis weight and size for example 2 are the same as example 1, but the caliper is greater than a targeted value of 16 points.

Handsheets were conditioned at a temperature (23±1° C.) and humidity (50±2%) at least overnight and tested for caliper (TAPPI T411), basis weight (TAPPI T410), tensile (TAPPI T220), ZDT tensile (TAPPI T541), ring crush (T818), Mullen burst (TAPPI T807) and STFI (T826). At least three replicates (n=3) were tested to produce averaged values reported for each parameter. All mechanical properties are comparable or better than those from the sample shown for example 1. It is surprising in particular that 100% wheat straw in the middle layer 10 showed enhanced mechanical strength such as ZD tensile and stiffness. The stiffness is the most important parameter for paperboard as it affects the ability of cartons to run smoothly through the machine that erects, fills, and closes them. Normally, the presence of non-wood alternative fiber will adversely affect mechanical properties of the composite paperboard.

TABLE 1 Three-Layered Handsheet Mechanical Properties Pine/Recylced [Pine-Bamboo 50/50]/ Pre-Consumer Wheat Straw/ IDENTIFICATION Fiber/Pine [Pine-Bamboo 50/50] Sample length, in. 12 12 Sample width, in. 7 7 Caliper, mils. 21.37 24.61 BW, lbs/1000 sq.ft. 57.53 59.98 Density, g/cc 0.517 0.468 STFI, lbs per Inch - MD 40.54 31.09 STFI, lbs per inch - CD 18.94 19.88 Mullen Burst, psi 197 138 Ring Crush, psi 1240 948 Ring Crush, psi 767 623 Stiffness, Taber units - MD 325 343 Stiffness, Taber units - CD 83 138 Tear, grams (force) - MD 340 262 Tear, grams (force) - CD 740 569 Tensile lbs/in - MD 114.46 96.72 Tensile lbs/in - CD 49.37 47.84 ZDT, lbs force 29 45

Example 3

This example uses a commercial paperboard sample, StarBlanc C1S Ivory board, as a control sample. It has the same multilayer composition as described in FIG. 1. However, all fibers used in the control sample are virgin wood pulp, where the middle layer 10 is made of 35% APMP, 30% BCTMP and 35% broke. The top and back layers 20, 30 are 15 to 25% NBKP and 75 to 85% LBKP. There are three layers of coating on the front side of the paperboard and one layer of coating on the reverse side. The basis weight is targeted to be 300 g/m². The weight distribution is about 58-65% for the middle layer 10, 14-15% for the top layer 20, and 11-12% for the back layer. The remainder is coating layers. The control paperboard testing parameters are listed in Table 2.

Examples 4

Bamboo pulp was used in this example to replace a portion of virgin wood pulp in top and back layers 20, 30. The top layer 20 used 25% NBKP and 75% bamboo. The back layer 30 used 15% NBKP and 85% bamboo. The paperboard made on PM 18 was tested under controlled temperature (23±1° C.) and relative humidity (50±2%). The results are shown in Table 2. In comparison to the control sample, folding strength is much better than for the control sample, whereas smoothness is about ½ of the control. The required smoothness is at least 100 or in a range of 150 and above.

These fiber ratios can be changed and yet still within the scope of the invention. For example, the top layer 20 can use 50% bamboo and 50% LBKP. Alternatively, the back layer 30 can use 30% bamboo and 70% LBKP, while keeping the middle layer 10 the same.

TABLE 2 Control and Sample Paperboard Testing Results Inspection Inspection items Unit method Example 1 Example 2 Grammage g/m² GB/T 451.2-2002 303 307 Banner grammage difference g/m² 6 4 Thickness μm GB/T 451.3-2002 415 415 Banner thickness difference % 1.2 2.9 Stiffness Cross direction mN. m GB/T22364-2008 6.2 6.3 ★Aspect ratio 2.6 2.6 Folding Longitudinal number of GB/T457-2008 51 117 strength Cross direction times 14 119 Surface roughness(TOP)PPS μm GB/T 22363-2008 0.55 0.54 Smoothness (TOP) s GB/T 456-2002 679 289 Whiteness (TOP) % GB/T 7974-2002 90.5 91.9 Whiteness (BACK) % 87.2 86.9 Glossiness (TOP) % GB/T 8941 55 54 Surface TOP g/m² GB/T 1540-2002 27.2 23.6 water BACK 29.8 25.6 Speckiness (0.3-1.5)mm² number/m² GB/T 1541-2007 0 0 >1.5 mm² 0 0 Hue (TOP)L GB/T 7975-2005 94.8 95.7 a 0.79 0.74 b −1.96 −1.87 (BACK)L 95.9 96.1 a −0.2 −0.44 b 2.26 2.93 Moisture % GB/T 462-2008 7.6 8.4 Printing surface strength m/s GB/T 22385-2008 0.75 1.2 Interlayer combination strength J/m² GB/T 26203-2010 190 193 Ink absorbency % GB/T 12911-91 23 22 Inspection conclusion: This paper can be classed as Grade A goods. Note: ★means the item is not used for grade estimation.

Example 5

The paperboard sample from Example 4 was mounted and cut into a broad ion beam (BIB) section for a cross-sectional view at MVA Scientific Consultant (Duluth, Ga.). The BIB cross sectioning is an advanced method for preparing accurate cross section surfaces for a wide variety of materials. BIB excels in comparison to traditional methods such as mechanical polishing or microtome when cross-sectioning soft materials, very hard materials, porous materials, or combinations of these. The BIB cross-sectioned surface area is approximately 1 mm in width and several hundred micrometers in length. The ion beam is able to cut through paperboard without deforming it or filling the pores. This allows for detailed studies of the pore structure, for example, how deep the filler such as calcium carbonate will penetrate into the porous coating layer.

A sample is first cut and trimmed for suitable size and shape. It is then attached to a sample holder (titanium) which acts as a mask plate. A small part (20-200 μm) of the sample is left visible above the edge of the mask. The broad argon ion beam is aligned perpendicular on the edge of the mask so that half of the beam hits the sample and the other half hits the mask. The ions start removing material from the visible area of the sample while the mask plate protects the rest. Over time the ion bombardment results in a clean planar cross section area of the sample behind the mask plate edge. As shown in FIG. 2, thick white layer is three layered calcium carbonate coating and thin layer is one layer calcium carbonate coating. The BCTMP portion fiber is layered in the middle and hollow. The top and back layers 20, 30 are a mixture of wood-based and bamboo fibers. These observations are further verified in FIG. 3, where SEM C-stain shows lignified BCTMP (yellow color) in the middle and delignified wood-based and bamboo fibers in the top and back layers 20, 30. Also, it is visible that the density of fibers changes across the paperboard thickness.

All percentages, parts and ratios are based upon the total weight of the compositions of the present disclosure, unless otherwise specified. All such weights as they pertain to listed ingredients are based on the active level and, therefore; do not include solvents or by-products that can be included in commercially available materials, unless otherwise specified. The term “weight percent” can be denoted as “wt. %” herein. Except where specific examples of actual measured values are presented, numerical values referred to herein should be considered to be qualified by the word “about.”

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm”.

All documents cited in the Detailed Description are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present disclosure. To the extent that any meaning or definition of a term in this written document conflicts with any meaning or definition of the term in a document incorporated by reference, the meaning or definition assigned to the term in this written document shall govern.

While particular aspects of the present disclosure have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the disclosure. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this disclosure. 

What is claimed is:
 1. A paperboard packaging material comprising: a top layer including non-wood fibers blended with wood fibers, wherein the non-wood fibers are 5% to 100% of the top layer; a back layer including non-wood fibers blended with wood fibers, wherein the non-wood fibers are 5% to 100% of the back layer; and a middle layer disposed between the top and back layers.
 2. The paperboard packaging material of claim 1, wherein the middle layer includes 5% to 100% non-wood filler fibers.
 3. The paperboard packaging material of claim 2, wherein the non-wood filler fibers are selected from corn stover, straw, other land-based natural fibers, and combinations thereof.
 4. The paperboard packaging material of claim 3, wherein the straw is selected from the group consisting of wheat, rice, oat, barley, rye, flax, grass, and combinations thereof.
 5. The paperboard packaging material of claim 3, wherein the other land-based natural fibers are selected from flax, bamboo, cotton, jute, hemp, sisal, bagasse, kenaf, hesperaloe, switchgrass, miscanthus, and combinations thereof.
 6. The paperboard packaging material of claim 2, wherein the non-wood filler fibers are wheat straw.
 7. The paperboard packaging material of claim 1, wherein the non-wood fibers are bamboo.
 8. The paperboard packaging material of claim 1, further comprising a coating on one or both of the top and back layers.
 9. The paperboard packaging material of claim 8, wherein the coating is selected from latex, kaolin clay, and calcium carbonate.
 10. The paperboard packaging material of claim 1, wherein the non-wood fibers are 50% to 85% of the top layer
 11. The paperboard packaging material of claim 1, wherein the non-wood fibers are 50% to 85% of the back layer.
 12. A paperboard packaging material comprising: a top layer including non-wood fibers blended with wood fibers, wherein the non-wood fibers are 50% to 85% of the top layer, wherein the non-wood fibers are bamboo; a back layer including non-wood fibers blended with wood fibers, wherein the non-wood fibers are 50% to 85% of the back layer, wherein the non-wood fibers are bamboo; and a middle layer disposed between the top and back layers.
 13. The paperboard packaging material of claim 12, wherein the middle layer includes 5% to 100% non-wood filler fibers.
 14. The paperboard packaging material of claim 13, wherein the non-wood filler fibers are selected from corn stover, straw, other land-based natural fibers, and combinations thereof.
 15. The paperboard packaging material of claim 13, wherein the straw is selected from the group consisting of wheat, rice, oat, barley, rye, flax, grass, and combinations thereof.
 16. The paperboard packaging material of claim 13, wherein the other land-based natural fibers are selected from flax, bamboo, cotton, jute, hemp, sisal, bagasse, kenaf, hesperaloe, switchgrass, miscanthus, and combinations thereof.
 17. The paperboard packaging material of claim 13, wherein the non-wood filler fibers are wheat straw.
 18. A paperboard packaging material comprising: a top layer including non-wood fibers blended with wood fibers, wherein the non-wood fibers are 50% to 85% of the top layer, wherein the non-wood fibers are bamboo; a back layer including non-wood fibers blended with wood fibers, wherein the non-wood fibers are 50% to 85% of the back layer, wherein the non-wood fibers are bamboo; and a middle layer disposed between the top and back layers, wherein the middle layer includes 5% to 100% non-wood filler fibers.
 19. The paperboard packaging material of claim 18, wherein the non-wood filler fibers are wheat straw. 